As is well known in the art, microprocessors are large scale integrated circuit devices. A microprocessor chip may contain the control unit, central processing circuitry, and arithmetic and logic circuitry for a computer, permitting its use as a single-chip computer component. As such, microprocessors generally constitute the primary computer element for a computer. Numerous circuit devices are necessary to assist the microprocessor in its function, such as memory chips (RAM and ROM), input-output chips, as well as conventional electrical devices such as diodes, capacitors, inductors and resistors. However, the microprocessor chip will typically be the most expensive single device on a circuit board.
Microprocessor chips are typically soldered to their circuit board, such as a ceramic substrate or printed wiring board. Due to the numerous functions performed by microprocessors, a relatively large number of terminals are required. The size of a typical microprocessor chip is generally on the order of a few millimeters per side, making it somewhat difficult to mount a microprocessor chip to its circuit board. A conventional method adopted by the industry is the flip-chip bonding process. This process utilizes a microprocessor chip referred to as a flip chip, which is generally a monolithic semiconductor device having bead-like terminals provided on one face of the chip. The terminals serve as connections between the microprocessor chip and a suitable conductor pattern formed on the circuit board. Flip chip conductor patterns are composed of numerous individual conductors, often as small as about 0.006 inch in width, and spaced about 0.008 inch apart. As a result, soldering a microprocessor flip chip to its conductor pattern requires a significant degree of precision.
Generally, early in the development of a microprocessor-based product which uses a microprocessor flip chip, the software code required for the fabrication of the production flip chip is not yet established. Consequently, for development purposes the production flip chip's software is typically simulated with a microprocessor emulator, such as a programmable, prepackaged integrated circuit. To do so, a substrate designer is required to design an engineering development unit with an integrated circuit socket mounted to the unit's substrate. A programmable, prepackaged integrated circuit can then be inserted into the socket, by which simulations can be performed for software development.
Unfortunately, integrated circuit sockets are generally many times larger than a microprocessor flip chip, such that an engineering development unit will be much larger than the eventual production unit. Consequently, after the software code has been established, the substrate designer must then specifically design a substrate for the production unit, which will utilize the microprocessor flip chip that dictates the production unit's conductor pattern.
Accordingly, a shortcoming of the above development process is the requirement that two separate substrates be designed for a single microprocessor-based product. Such a requirement adds significantly to the time required to arrive at a final production design for the product. Furthermore, the mounting features of an integrated circuit package which incorporates the product, as well as the mounting site within its ultimate working environment, cannot be determined until the size of the final production unit has been established. As a result, the final implementation of the product is further delayed until such considerations have been resolved.
From the above, it can be seen that it would be desirable if an electronic circuit board which employs a microprocessor flip chip could be developed without the requirement that a development unit be specially designed to accommodate an integrated circuit socket. Conventionally, to do so would require an emulator, such as a programmable, prepackaged integrated circuit, which corresponds in size and shape to the intended production flip chip for the circuit board. However, the prior art has generally been discouraged from seeking such a solution due to the extremely small size and the intricate configuration of a flip chip conductor pattern to which such an emulator would need to be connected.
Accordingly, what is needed is a method by which a suitable interconnecting device can be mated with the conductor pattern for a production flip chip on the substrate of an engineering development unit, so as to enable the unit to be tested and evaluated without requiring an integrated circuit socket to be present on the circuit board. Such an interconnecting device would serve to connect a microprocessor emulator to the unit to simulate a microprocessor, while various development tests and/or evaluations are performed. As a result, the engineering development unit could be designed to accommodate the production flip chip and its conductor pattern, so as to allow the design of a single substrate which can be used for both the development unit and the final production units.